The overall objectives are to clarify the physiological functions and pharmacological actions of hormones affecting calcium metabolism and to relate this information to problems in diagnosis and treatment of disease. Principal attention is directed at parathyroid hormone (PTH) and thyrocalcitonin (TC) and their interrelations with the adrenal gland, gastrointestinal hormones, and vitamin D. Specific current projects include: 1. Preparation of additional supplies of pure rat TC for determination of amino acid sequence, and further development of radioimmunoassay for rat TC. 2. Mechanism of enhancement of hypocalcemic effect of TC in stress. 3. Procedures for preserving TC in rat thyroid glands so they can be stored for assay. 4. Production of experimental cardiovascular calcification, protective action of TC against this condition, and investigation of effect of age on susceptibility. 5. Protective effect of TC against nephrocalcinosis produced by diet. 6. Electron microscopic study of mechanisms of TC release. 7. Effect of sialadenectomy on serum Ca in thyroparathyroidectomized rats. 8. Effect of iodine deficiency in rats on C-cells and thyroid TC content. 9. Investigation of G-I hormones as mediators between G-I Ca and TC secretion. 10. Investigation of G-I hormonal factors in TC secretion during feeding. 11. Development of antisera to human TC in rats.